What is React?

React, also known as React.js or ReactJS, is a powerful JavaScript library for building user interfaces, particularly single-page applications (SPAs) where you need a fast, interactive user experience. Originally developed by Facebook in 2011 for its news feed feature, React has since been open-sourced and is maintained by Facebook and a community of individual developers and companies.

Core Concepts of React


React code is made of entities called components. Components are JavaScript classes or functions that optionally accept inputs, called props, and return a React element that describes how a section of the UI should appear. The encapsulated nature of React components makes them reusable, promoting a "write once, use many times" approach.


React embraces the concept of JSX (JavaScript XML), which allows you to write HTML-like syntax directly in your JavaScript code. It is not a necessity to use JSX in React, but it is the recommended way of describing what the UI should look like.

function Hello() {
  return <h1>Hello, world!</h1>;

The Virtual DOM

One of the key aspects that makes React so performant is the concept of the Virtual DOM. Every time a React component's state changes, a new virtual DOM representation of the user interface is created. React then compares this new representation with the previous one and smartly updates only the parts of the real DOM that changed. This diffing process makes React applications incredibly fast and efficient.

The Power of React

React has gained significant popularity among developers and companies worldwide due to its efficiency, flexibility, and strong community support. Here are some reasons why:

  1. Easy to Learn and Use: If you already know JavaScript, picking up React can be straightforward. Its component-based approach can be easily grasped and allows for the creation of complex user interfaces from simple, isolated pieces of code.
  2. Reusable Components: Components can be reused across different parts of an application, making development faster and the code more manageable.
  3. Fast and Efficient: The Virtual DOM allows React to update only the parts of the app that need to change when the state updates, making it highly efficient.
  4. Strong Community and Rich Ecosystem: React has a large and active community, which means that there are plenty of resources, such as tutorials and third-party libraries, available. It also implies better opportunities for getting help and support.
  5. Backed by Facebook: React is used in production at Facebook and Instagram, and it's actively maintained by Facebook, which gives developers confidence in its longevity and continued support.

React, with its robust ecosystem, large community, and strong backing from Facebook, offers a great choice for developers looking to build modern, interactive web applications.